Non-woven textiles formed from polymers are useful materials for a variety of applications including, but not limited to, general textile applications and specialty applications such as scaffolding materials for tissue engineering. In scaffold design for tissue engineering applications, porosity is a significant parameter to evaluate when gauging the success of a particular scaffold because the cellular environment is crucial to cell viability and migration. Porous biomaterial structures have been formed using techniques such as three-dimensional patterning through stereolithography, phase separation, solvent casting/particulate leaching, gas foaming, and electrospinning. Electrospinning is an attractive technique for forming polymer scaffolds for tissue engineering as it produces a network of fibers of the same order of magnitude as the biological molecules found in the extracellular matrix. Furthermore, although electrospinning is a simple technique to produce fibers with nanometer to micrometer dimensions, there are many variables including solution concentration, applied voltage, needle gauge, and collector distance which influence the morphology of the produced fibers. Accordingly, electrospinning is a technique which allows for significant fine tuning of the final product, by alteration of these various factors. However, until now, it has not been possible to electrospin polymers having a low glass transition temperature (Tg) or low melting point (Tm). Furthermore, electrospinning techniques have previously only been successfully applied to polymers having a high molecular weight.
Poly(propylene fumarate) (PPF) is an unsaturated polyester which has a low melting point (it is liquid at room temperature) and which has been shown to be both biocompatible and biodegradable, having biocompatible degradation products and mechanical properties similar to bone when covalently crosslinked. Because of these properties, PPF has been explored extensively as a scaffold for bone tissue engineering. PPF can be crosslinked thermally or photochemically via the fumarate carbon-carbon double bond, and accordingly, in addition to tissue engineering scaffolds, PPF has been shown to be a promising polymer to use in bone cements where the polymer is applied as a composite forming a putty-like mixture that can be hardened via crosslinking of the fumarate bond. Because PPF is liquid at room temperature, this polymer is particularly attractive for bio-engineering purposes as it can be injected, along with a leachable porogen, into an irregularly shaped defect site and crosslinked in situ. However, due to its low Tg and low Tm, polymers like PPF have not been successfully electrospun.
Previous attempts to form fibers from polymers having low molecular weight and either a low Tg or low Tm have being entirely unsuccessful (See e.g, Song, T.; Zhang, Y. Z.; Zhou, T. J. Fabrication of magnetic composite nanofibers of poly(ε-caprolactone) with FePt nanoparticles by coaxial electrospinning. Journal of Magnetism and Magnetic Materials (2006), 303(2), e286-e289, hereby incorporated by reference). Methods that did succeed, required a high molecular weight polymer or relied on encasing the low Tg polymer material in a high Tg polymer—producing a hybrid material containing both high and low Tg polymers or oligomers. When it was desirable to form a material consisting only of the low Tg or Tm polymer, it was necessary to perform an additional step of removing the high Tg or Tm polymer after fiber formation. (See e.g., McCann Jesse T; Marquez Manuel; Xia Younan Melt coaxial electrospinning: a versatile method for the encapsulation of solid materials and fabrication of phase change nanofibers. Nano letters (2006), 6(12), 2868-72.)
Other methodologies for electrospinning non-woven fiber mats from high molecular weight, low Tg or Tm polymers have relied on chemically modifying the polymer prior to electrospinning (Cashion, M. P.; Brown, R. H.; Mohns, B. R.; Long, T. E., Abstract of Papers, 238th ACS National Meeting, Washington, D.C., United States, Aug. 16-20, 2009, POLY 2009) or were successful only with rubber polymers (Choi, S. S.; Hong, J. P.; Seo, Y. S.; Chung, S. M.; Nah, C., J. Appl. Polym. Sci. 101, 2333 2006).
Accordingly, methodologies which allow for materials including oligomers and some monomers and polymers having characteristics such as low molecular weight, low Tg, and/or low Tm, which have previously made them unsuitable for electrospinning, to be formed into fibers for production of non-woven textiles are greatly desired.